Rectangular Marquee tool


Open a picture
Select the rectangular maarquee too - second from the top
Select an area on your picture that is rectangular and drag the rectangular marquee tool across it to make a rectangle
When you let themouse go you can use your cursor keys to fine tune the shape and you can use the shift keys with the cursor keys
Because an area is selected - any commands will also only be applied to that area.
eg select layer - new adjustment layer - photo filterok
select cooling filter - density - area will turn light blue.